For a single phase half-wave thyristor circuit with R load, the power delivered to the resistive load is

(average load voltage) x (average load current)

In a three phase dual converter, converter 1 is operating with α = 95° and converter 2 is operating with α2 = 85°. Choose the correct statement.

Both the converters are operating as an inverter

Converter 1 is operating as a rectifier and converter 2 as an inverter

Both the converters are operating as a rectifier

Converter 1 is operating as a inverter and converter 2 as an rectifier

Both the converters are operating as an inverter

A three-phase three-pulse converter would operate as a line commutated inverter when

it can never operate as a line commutated inverter

In case of controlled rectifiers, the nature of the load current (continues or discontinuous) depends upon the

it is independent of all the parameters

A semi-converter with RLE load and a freewheeling diode has discontinuous load current with firing angle α and extinction angle β. If β < π and Vm sinβ < E then

the converter operates as a line commutated inverter

the conduction period is absent

the freewheeling period is absent

Consider the following statement:The overlap angle of a phase controlled converter will increase ___________i) if the firing angle is increasedii) if the supply frequency is increasedii) if the supply voltage magnitude is loweredOf these statements

only the first and the last one are correct

only the first one is incorrect

A single-phase two pulse converter feeds RL load with a sufficient smoothing such that the load current does not fall to zero. If the resistance of the load circuit is increased then the

ripple content of current decreases

ripple content of current increases

ripple content of current decreases

Choose the incorrect statement with respect to the use of FD in half-wave circuits.

Load current waveform is improved

It prevents the load voltage from becoming negative

Reduces the reverse voltage (PIV) faced by the SCR

When a line commutated converter operates in the inverter mode then

it delivers reactive power to the supply

it draws real and reactive power from the supply

it delivers both real and reactive power to the supply

it delivers real power to the supply

it delivers reactive power to the supply

For a single phase half-wave thyristor circuit with R load, the input power factor is given by

rms source voltage/total rms line current

rms input power/power delivered to the load

power delivered to load/input VA

In a single phase full converter with resistive load and firing angle α, the load current is

remains zero for duration π-α

Which of the following converter circuits would require a neutral point?

3-phase full converter with freewheeling diode

If in the below given converter configuration, any 3 of the 4 SCRs are replaced by diodes

the average output voltage would decrease

the average output voltage would increase

the average output voltage would decrease

the average output voltage would not change

For the same triggering angle and ratings

a semi-converter has lower values of input p.f as compared to a full converter

a semi-converter operates at lower output voltage than a full converter

a semi-converter operates at higher output voltage than a full converter

a semi-converter has lower values of input p.f as compared to a full converter

a semi-converter has more THD as compared to a full converter

A single-phase asymmetrical semi-converter employs

one SCR and one diode in each leg

two SCRs in one leg and two diodes in the other

151 + Mcqs in Converters in Power Electronics Page 3 McqOptions

101.	A three-phase three pulse type controlled converter is constructed using 3 SCR devices. The circuit is supplying an R load with α < 30°. As such, each SCR device would conduct for
A.	60° each cycle
B.	120° each cycle
C.	180° each cycle
D.	360° each cycle
Answer» C. 180° each cycle

Discussion

102.	For a single phase half-wave thyristor circuit with R load, the power delivered to the resistive load is
A.	(average load voltage) x (average load current)
B.	(rms supply voltage)2/R
C.	(rms load voltage)2/R
D.	(average load voltage)/R
Answer» D. (average load voltage)/R

Discussion

103.	A motor load is connected to a single-phase full converter B-2 type controlled rectifier. The net energy is transferred from ac source to the motor (dc load) when
A.	π+α > 90
B.	π-α > α
C.	π+α > α
D.	π-α > 90
Answer» C. π+α > α

Discussion

104.	An SCR has the peak forward voltage = 1000 V. Find the maximum voltage that the SCR can handle if employed in a M-2 type full controlled converter circuit. Use factor of safety (FOS) = 2.5
A.	500 V
B.	400 V
C.	200 V
D.	1000 V
Answer» D. 1000 V

Discussion

105.	A single-phase full converter bridge, is connected to a RLE load. The source has a rms voltage of 230 V and the average load current is 10 A. Find the firing angle for which the power flows from the DC load to the AC source. Consider E = 120 V, R = 0.4 Ω, L = 2 Henry.
A.	124°
B.	153°
C.	142°
D.	309°
Answer» B. 153°

Discussion

106.	In a B-2 type full controlled bridge converter
A.	one SCR conducts at a time
B.	two SCRs conduct at a time
C.	three SCRs conduct at a time
D.	four SCRs conduct at a time
Answer» C. three SCRs conduct at a time

Discussion

107.	The PIV for each diode in a single-phase, full converter with B-2 type of controlled rectifier isConsider supply voltage as Vs = Vm sinωt.
A.	2Vm
B.	Vm
C.	Vm/2
D.	Vm/√2
Answer» C. Vm/2

Discussion

108.	In a p-pulse converter, each SCR conducts for (per cycle)
A.	p radians
B.	p degrees
C.	p/2π radians
D.	2π/p radians
Answer» E.

Discussion

109.	A single-phase full converter bridge, is connected to a RLE load. The source has a rms voltage of 230 V and the average load current is 10 A. Find the firing angle for which the power flows from AC source to the DC load. Consider E = 120 V, R = 0.4 Ω.
A.	26.4°
B.	53.2°
C.	142°
D.	39°
Answer» C. 142°

Discussion

110.	In a three phase dual converter, converter 1 is operating with α = 95° and converter 2 is operating with α2 = 85°. Choose the correct statement.
A.	Converter 1 is operating as a rectifier and converter 2 as an inverter
B.	Both the converters are operating as a rectifier
C.	Converter 1 is operating as a inverter and converter 2 as an rectifier
D.	Both the converters are operating as an inverter
Answer» D. Both the converters are operating as an inverter

Discussion

111.	An SCR has the peak forward voltage = 1000 V. Find the maximum voltage that the SCR can handle if employed in a B-2 type full controlled converter circuit. Use factor of safety (FOS) = 2.5
A.	500 V
B.	400 V
C.	200 V
D.	1000 V
Answer» C. 200 V

Discussion

112.	A three-phase semi-converter circuit is given a supply of 400 V. It produces at the output terminals an average voltage of 381 V. Find the rectification efficiency of the converter circuit.
A.	0.9965
B.	0.9525
C.	0.91
D.	0.865
Answer» C. 0.91

Discussion

113.	A three-phase three-pulse converter would operate as a line commutated inverter when
A.	30° < α < 60°
B.	90° < α <180°
C.	90° > α
D.	it can never operate as a line commutated inverter
Answer» C. 90° > α

Discussion

114.	In case of controlled rectifiers, the nature of the load current (continues or discontinuous) depends upon the
A.	type of load and firing angle
B.	only on the type of load
C.	only on the firing angle
D.	it is independent of all the parameters
Answer» B. only on the type of load

Discussion

115.	A single-phase half wave circuit has Vs = 230 V with a R load of 100 Ω. Find the average load current at α = 30°.
A.	1.45 A
B.	0.57 A
C.	0.96 A
D.	2.3 A
Answer» D. 2.3 A

Discussion

116.	In a 3-phase full wave converter, if V is the maximum value of line voltage at the input, then each SCR is subjected to a peak negative voltage of
A.	V
B.	3V
C.	√3V
D.	V/2
Answer» D. V/2

Discussion

117.	A single phase full converter feeds power to a RLE load with R = 6 Ω and E = 60 V. Find the average value of the load current when the supply voltage is 230 V rms AC and a firing angle = 50°.
A.	0
B.	3.9A
C.	12.1 A
D.	6.05 A
Answer» D. 6.05 A

Discussion

118.	A semi-converter with RLE load and a freewheeling diode has discontinuous load current with firing angle α and extinction angle β. The freewheeling period is
A.	π>ωt<β
B.	π>ωt<β
C.	π<ωt>β
D.	π>ωt>β
Answer» B. π>ωt<β

Discussion

119.	A semi-converter with RLE load and a freewheeling diode has discontinuous load current with firing angle α and extinction angle β. If β < π and Vm sinβ < E then
A.	the converter operates as a line commutated inverter
B.	the conduction period is absent
C.	the freewheeling period is absent
D.	none of the mentioned
Answer» D. none of the mentioned

Discussion

120.	A voltage source Vs = Vm sinωt is connected in series with a resistance R and an SCR. At some firing angle delay of α a positive gate pulse is applied to the SCR which turns on the SCR. Considering ideal conditions, at the instant α the voltage at the resistor terminals Vo
A.	falls to zero
B.	falls to -Vm sin α
C.	rises to Vm sin α
D.	rises to Vm sin ωt
Answer» D. rises to Vm sin ωt

Discussion

121.	A three-phase full converter supplied from a 230 V source is working as a line commutated inverter. The load consists of RLE type with R = 5 Ω, E = 200 V and L = 1 mH. A continues current of 10 A is flowing through the load, find the value of the firing angle delay.
A.	119°
B.	127°
C.	156°
D.	143°
Answer» B. 127°

Discussion

122.	Semi-converters are
A.	single quadrant converters
B.	double quadrant converters
C.	three quadrant converters
D.	none of the mentioned
Answer» B. double quadrant converters

Discussion

123.	A single-phase semi-converter is operated from a 240 V, 60 Hz, AC source. It is fired at an angle of 45°. Find the value of average output voltage.
A.	176 V
B.	184 V
C.	167 V
D.	148 V
Answer» C. 167 V

Discussion

124.	A single phase 230 V, 1 kW heater is connected across a 1-phase 230 V, 50 Hz supply through an SCR. The firing angle of the SCR is adjusted to give a rms voltage of 155 V. Find the power absorbed by the heater element.
A.	250 watts
B.	1 kW
C.	454 watts
D.	378 watts
Answer» D. 378 watts

Discussion

125.	Consider the following statement:The overlap angle of a phase controlled converter will increase ___________i) if the firing angle is increasedii) if the supply frequency is increasedii) if the supply voltage magnitude is loweredOf these statements
A.	all are correct
B.	only the first and the last one are correct
C.	only the first one is incorrect
D.	all are incorrect
Answer» D. all are incorrect

Discussion

126.	For a single-phase dual converter, with converters C1 and C2 connected in anti-parallel, which relation among the following is true to keep the average voltages from C1 and C2 equal? C1 and C2 have firing angles α1 and α2 respectively.
A.	α1 = α2
B.	α1 + α2 = 360°
C.	α1 + α2 = 180°
D.	none of the mentioned
Answer» D. none of the mentioned

Discussion

127.	A single-phase two pulse converter feeds RL load with a sufficient smoothing such that the load current does not fall to zero. If the resistance of the load circuit is increased then the
A.	ripple content is not affected
B.	ripple content of current increases
C.	ripple content of current decreases
D.	load current may fall to zero
Answer» C. ripple content of current decreases

Discussion

128.	Choose the incorrect statement with respect to the use of FD in half-wave circuits.
A.	Input pf is improved
B.	Load current waveform is improved
C.	It prevents the load voltage from becoming negative
D.	Reduces the reverse voltage (PIV) faced by the SCR
Answer» E.

Discussion

129.	In case of a single-phase half-wave circuit with RL load, with firing angle α and extinction angle β, the thyristor is reversed biased from
A.	β to α
B.	β to 2π+α
C.	β to 2π
D.	β to 2β
Answer» D. β to 2β

Discussion

130.	A single-phase semi-converter is connected to a 230 V source and is feeding a load R = 10 Ω in series with a large inductance that makes the load current ripple free. For α = 45°, find the rectification efficiency. The RMS value of output voltage is 219.3 V
A.	0.9654
B.	0.7525
C.	0.8945
D.	0.8058
Answer» E.

Discussion

131.	A 3-phase bridge converter is given a three-phase supply in the phase sequence R-Y-B. Let the neutral to R phase voltage be Vm sinωt. The first SCR (connected to R phase) is fired at an angle of 15°. What is the maximum value at the output terminals at this instant?
A.	Vm/√2
B.	Vm
C.	1.5 Vm
D.	3 Vm
Answer» D. 3 Vm

Discussion

132.	In case of three-phase dual converter, one of the converter circuits is fired at an angle of 60°. For both the converter circuits to have equal average output voltage, what is the value of the firing angle for the other converter circuit?
A.	60°
B.	120°
C.	100°
D.	Insufficient data
Answer» C. 100°

Discussion

133.	When a line commutated converter operates in the inverter mode then
A.	it draws real and reactive power from the supply
B.	it delivers both real and reactive power to the supply
C.	it delivers real power to the supply
D.	it delivers reactive power to the supply
Answer» D. it delivers reactive power to the supply

Discussion

134.	In non-circulating current mode dual converters, the circulating current is avoided by
A.	connecting a series reactor
B.	maintaining α1 + α2 = 180°
C.	operating only one converter
D.	adding an extra SCR
Answer» D. adding an extra SCR

Discussion

135.	For a single phase half-wave thyristor circuit with R load, the input power factor is given by
A.	rms source voltage/total rms line current
B.	rms input power/power delivered to the load
C.	cos α
D.	power delivered to load/input VA
Answer» E.

Discussion

136.	In a single phase full converter with resistive load and firing angle α, the load current is
A.	zero at α, π+α, …
B.	remains zero for duration α
C.	Vm/R sinα at α, π+α, …
D.	remains zero for duration π-α
Answer» D. remains zero for duration π-α

Discussion

137.	In a single phase full converter, for discontinuous load current and extinction angle β > π, each SCR conducts for
A.	α
B.	β
C.	β-α
D.	β+α
Answer» D. β+α

Discussion

138.	The average output voltage is maximum when SCR is triggered at ωt =
A.	π
B.	0
C.	π/2
D.	π/4
Answer» C. π/2

Discussion

139.	The range of firing angle for a 3-phase, 3-pulse converter feeding a resistive load is __________ (in degrees).
A.	0 to 180
B.	0 to 150
C.	30 to 150
D.	30 to 180
Answer» C. 30 to 150

Discussion

140.	A single-phase half wave rectifier with a FD is supplied by Vs = 240 V, AC with a load R = 10 Ω, L = 0.5 mH and a firing angle α = 30°. Find the average value of the load voltage.
A.	50 V
B.	100 V
C.	150 V
D.	200 V
Answer» C. 150 V

Discussion

141.	Which of the following converter circuits would require a neutral point?
A.	3-phase semi-converter
B.	3-phase full converter
C.	3-phase full converter with freewheeling diode
D.	3-phase half wave converter
Answer» E.

Discussion

142.	Consider the following statements regarding phase controlled converters:i) They do not provide smooth variation of output voltage.ii) They inject harmonics into the power system.iii) They draw non-unity power factor current for finite firing angles.Which of the above statements are correct?
A.	All the three
B.	i and ii only
C.	i and iii only
D.	ii and iii only
Answer» B. i and ii only

Discussion

143.	A 3-phase full converter delivers a ripple free load current of 10 A with a firing angle delay of 45°. Find the DF (distortion factor).
A.	1.414
B.	0
C.	0.707
D.	0.569
Answer» D. 0.569

Discussion

144.	A 3-phase full converter has an average output voltage of 365 V for zero degree firing and resistive load. For a firing angle of 90 degree, the output voltage would be
A.	125 V
B.	569 V
C.	365 V
D.	zero
Answer» E.

Discussion

145.	If in the below given converter configuration, any 3 of the 4 SCRs are replaced by diodes
A.	the average output voltage would increase
B.	the average output voltage would decrease
C.	the average output voltage would not change
D.	the circuit would malfunction
Answer» B. the average output voltage would decrease

Discussion

146.	For the same triggering angle and ratings
A.	a semi-converter operates at lower output voltage than a full converter
B.	a semi-converter operates at higher output voltage than a full converter
C.	a semi-converter has lower values of input p.f as compared to a full converter
D.	a semi-converter has more THD as compared to a full converter
Answer» C. a semi-converter has lower values of input p.f as compared to a full converter

Discussion

147.	Find the expression of the rms value of output voltage for a single-phase M-2 type rectifier with RL load and continues load current. Transformer ratio is 1:1 with supply voltage Vs = Vm sinωt
A.	Vm/√2
B.	Vs
C.	2Vs
D.	Vs/√2
Answer» C. 2Vs

Discussion

148.	A single-phase asymmetrical semi-converter employs
A.	one SCR and one diode in each leg
B.	two SCRs in one leg and two diodes in the other
C.	two SCRs in both the legs
D.	two diodes in both the legs
Answer» C. two SCRs in both the legs

Discussion

149.	A single-phase semi-converter is having continuous conduction, as such each thyristor will conduct for an angle of
A.	α
B.	π
C.	α+π
D.	π-α
Answer» E.

Discussion

150.	A single-phase half-wave thyristor circuit with R load is triggered at an angle of α = 0°. As such, the maximum value of the average output voltage would be given byConsider Vs = Vm sinωt.
A.	Vm
B.	2Vm/π
C.	Vm/π
D.	Vm/α
Answer» D. Vm/α

Discussion

Explore topic-wise MCQs in Power Electronics.

A three-phase three pulse type controlled converter is constructed using 3 SCR devices. The circuit is supplying an R load with α < 30°. As such, each SCR device would conduct for

For a single phase half-wave thyristor circuit with R load, the power delivered to the resistive load is

A motor load is connected to a single-phase full converter B-2 type controlled rectifier. The net energy is transferred from ac source to the motor (dc load) when

An SCR has the peak forward voltage = 1000 V. Find the maximum voltage that the SCR can handle if employed in a M-2 type full controlled converter circuit. Use factor of safety (FOS) = 2.5

A single-phase full converter bridge, is connected to a RLE load. The source has a rms voltage of 230 V and the average load current is 10 A. Find the firing angle for which the power flows from the DC load to the AC source. Consider E = 120 V, R = 0.4 Ω, L = 2 Henry.

In a B-2 type full controlled bridge converter

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In a p-pulse converter, each SCR conducts for (per cycle)

A single-phase full converter bridge, is connected to a RLE load. The source has a rms voltage of 230 V and the average load current is 10 A. Find the firing angle for which the power flows from AC source to the DC load. Consider E = 120 V, R = 0.4 Ω.

In a three phase dual converter, converter 1 is operating with α = 95° and converter 2 is operating with α2 = 85°. Choose the correct statement.

An SCR has the peak forward voltage = 1000 V. Find the maximum voltage that the SCR can handle if employed in a B-2 type full controlled converter circuit. Use factor of safety (FOS) = 2.5

A three-phase semi-converter circuit is given a supply of 400 V. It produces at the output terminals an average voltage of 381 V. Find the rectification efficiency of the converter circuit.

A three-phase three-pulse converter would operate as a line commutated inverter when

In case of controlled rectifiers, the nature of the load current (continues or discontinuous) depends upon the

A single-phase half wave circuit has Vs = 230 V with a R load of 100 Ω. Find the average load current at α = 30°.

In a 3-phase full wave converter, if V is the maximum value of line voltage at the input, then each SCR is subjected to a peak negative voltage of

A single phase full converter feeds power to a RLE load with R = 6 Ω and E = 60 V. Find the average value of the load current when the supply voltage is 230 V rms AC and a firing angle = 50°.

A semi-converter with RLE load and a freewheeling diode has discontinuous load current with firing angle α and extinction angle β. The freewheeling period is

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A voltage source Vs = Vm sinωt is connected in series with a resistance R and an SCR. At some firing angle delay of α a positive gate pulse is applied to the SCR which turns on the SCR. Considering ideal conditions, at the instant α the voltage at the resistor terminals Vo

A three-phase full converter supplied from a 230 V source is working as a line commutated inverter. The load consists of RLE type with R = 5 Ω, E = 200 V and L = 1 mH. A continues current of 10 A is flowing through the load, find the value of the firing angle delay.

Semi-converters are

A single-phase semi-converter is operated from a 240 V, 60 Hz, AC source. It is fired at an angle of 45°. Find the value of average output voltage.

A single phase 230 V, 1 kW heater is connected across a 1-phase 230 V, 50 Hz supply through an SCR. The firing angle of the SCR is adjusted to give a rms voltage of 155 V. Find the power absorbed by the heater element.

Consider the following statement:The overlap angle of a phase controlled converter will increase ___________i) if the firing angle is increasedii) if the supply frequency is increasedii) if the supply voltage magnitude is loweredOf these statements

For a single-phase dual converter, with converters C1 and C2 connected in anti-parallel, which relation among the following is true to keep the average voltages from C1 and C2 equal? C1 and C2 have firing angles α1 and α2 respectively.

A single-phase two pulse converter feeds RL load with a sufficient smoothing such that the load current does not fall to zero. If the resistance of the load circuit is increased then the

Choose the incorrect statement with respect to the use of FD in half-wave circuits.

In case of a single-phase half-wave circuit with RL load, with firing angle α and extinction angle β, the thyristor is reversed biased from

A single-phase semi-converter is connected to a 230 V source and is feeding a load R = 10 Ω in series with a large inductance that makes the load current ripple free. For α = 45°, find the rectification efficiency. The RMS value of output voltage is 219.3 V

A 3-phase bridge converter is given a three-phase supply in the phase sequence R-Y-B. Let the neutral to R phase voltage be Vm sinωt. The first SCR (connected to R phase) is fired at an angle of 15°. What is the maximum value at the output terminals at this instant?

In case of three-phase dual converter, one of the converter circuits is fired at an angle of 60°. For both the converter circuits to have equal average output voltage, what is the value of the firing angle for the other converter circuit?

When a line commutated converter operates in the inverter mode then

In non-circulating current mode dual converters, the circulating current is avoided by

For a single phase half-wave thyristor circuit with R load, the input power factor is given by

In a single phase full converter with resistive load and firing angle α, the load current is

In a single phase full converter, for discontinuous load current and extinction angle β > π, each SCR conducts for

The average output voltage is maximum when SCR is triggered at ωt =

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Which of the following converter circuits would require a neutral point?

Consider the following statements regarding phase controlled converters:i) They do not provide smooth variation of output voltage.ii) They inject harmonics into the power system.iii) They draw non-unity power factor current for finite firing angles.Which of the above statements are correct?

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If in the below given converter configuration, any 3 of the 4 SCRs are replaced by diodes

For the same triggering angle and ratings

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A single-phase asymmetrical semi-converter employs

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